Hammer mill screen changing mechanism



1954 A. G. NICKLE HAMMER MILL SCREEN CHANGING MECHANISM 7 Sheets-Sheet 1Filed Sept. 27, 1949 IN V EN TOR.

Feb. 16, 1954 5 NlCKLE 2,669,396

HAMMER MILL SCREEN CHANGING MECHANISM Filed Sept. 27, 1949 7Sheets-Sheet 2 I NV EN TOR.

M3 N3 %w\ a 1954 A. G. NICKLE HAMMER MILL SCREEN CHANGING MECHANISM '7Sheets-Sheet 5 Filed Sept. 27, 1949 INVENTOR.

mm mwm mm C Feb. 16, 1954 A. G. NICKLE HAMMER MILL. SCREEN CHANGINGMECHANISM 7 Sheets-Sheet 4 Filed Sept. 2'7, 1949 FIB EI I N VEN TOR.

A. G. NICKLE HAMMER MILL SCREEN CHANGING MECHANISM Feb. 16, 1954 7Sheets-Sheet 5 Filed Sept. 27, 1949 IN V EN TOR.

Feb. 16, 1954 NlCKLE 2,669,396

HAMMER MILL SCREEN CHANGING MECHANISM Filed Sept. 27, 1949 7Sheets-Sheet 6 IN V EN TOR.

Feb. 16, 1954 A NICKLE HAMMER MILL SCREEN CHANGING MECHANISM 7Sheets-Shae Filed Sept. 2'7, 1949 mmm 3 A\ \ww MN I Q .1: m.

- INVENTOR. BY WW Patented Feb. 16, 1954 HAMMER MILL- SCREEN 5 GHANGING-MECHANISM Arthur G. N ickle,. Saginaw, Mich., assignor. to NickleEngineering, Saginaw, Mich.

Application September 27, 1948, Serial No. 51,433

40 Claims.

My invention relates to a mechanism for automatically interchanging anidle screen with a working screen in a hammer type grinding mill byremote electrical control. More especially my invention is applicable tohammer mills used in custom feed-grinding plants that process ear cornand small grain to produce livestock feeds of any desired fineness. Thehammer mills in general use in such plants are: installed below theoperating floor, so that the operator is compell'ed to travel up anddown from one floor to th'eother to manually change the Working screenwhen the fineness of the reduced material must be modified to suitindividual customers. Such manual screen-changing operations not onlyentail extra work. for the operator and a. loss of valuable time, but awaste of mill power, especially so if the mill must be stopped. andstarted to change the screen.

This invention provides an electrically controlled mechanism forremoving the working screen from a hammer-grinding mill, which screen isone of a plurality of similar screens interchangeable therewith, andautomatically replacing it by any idle screen selected from theplurality. To effect the screen interchange the operator simply pressesthe electrical pushloutton that is associated with the. selected screenthat is to be introduced into the mill housing. As the. automatic screeninterchange cycle involves a time interval of less than nine seconds, itwill be apparent that this invention affords a valuable means forconserving time and mill power when.

the fineness of the reduced product must be modilied.

A detailed description of this automatic screenchanging mechanism, asapplied to a hammer mill grinding unit, is made with reference to theaccompanying drawings in which is embodied one form of my invention.

Description of figures:

Fig. l is a side elevation of a hammer-grinding mill unit that embodiesthe automatic screenchanging mechanism.

Fig. 2 is a fragmentary plan view that corresponds to Fig. 1.

Fig. 3 is a fragmentary vertical transaxial sectional view through thegrinding chamber of the mill which shows the grading screen clamped inworking relation with the hammer rotative element and the idle screensmounted above the mill'housing, the view being indicated by line 3-4 inFig. 2.

Fig; 4 is an enlarged detail elevational view of abellcrank employed inthe screen-clamping mechanism.

Fig. 5 is an edgeview of the bellcrank shown in Fig. 4.

Fig. 6 is a fragmentary vertical sectional view showing screen-clampingand screen-translating means, the view being taken on line 6-5' of Fig.1.

Fig. 7 is a fragmentary sectional elevation of the screen-clampingmechanism taken on line 7---'! of Fig. 6, the clamping mechanism beingshown in the released position it assumes when the screen is entering orbeing withdrawn from the mill housing.

Fig. 8 is a fragmentary plan view showing how the upper end of one ofthe screens is attached to the screen-translating chains.

Fig. 9 is a side view of the chain and attachment shown in Fig. 8.

Fig. 10 is a fragmentary sectional view taken on line l0l0 of Fig. 8.

Fig. 11 is an exploded isometric view showing details of the slipclutchdriving mechanism employed in delivering power to the screen-clampingand screen-translating mechanisms.

Fig. 12 is a side elevational view showing in assembly the tracks. andsprocket wheels employed in guiding the several screen-translatingchains on one side of the mill housing.

Fig. 13 is an enlarged detailed sectional elevation of the trackassembly taken on line l3-l3 of Fig. 12.

Fig. 14 is an enlarged sectional elevation of the track assembly takenon line M-I 4 of Fig. 12.

Fig. 15 is an enlarged sectional elevation taken on line I5-|5 of Fig.12 showing the chain tighteners.

Fig. 16 is a fragmentary enlargement of one of the track plates shown inFig. 14 with the addition of a screen-translating chain mounted thereon.

Fig. 17 is a vertical sectional view taken on line l l--ll of Fig. 3showing the solenoids associated with the screen-restraining latches.

Fig; 18 is an electrical Wiring diagram showing remote controls appliedto motor that operates the screen-changing mechanism.

Description of hammer-grinding mill and auxiliary equipment vates itthrough pipe I3 to a dust collector (not shown). The crusher-feeder H],which is driven by V-belts I4 from motor l5,reduces the ungroundmaterials, such as ear corn, to a particle size that promotes accurateflow regulation to the grinding mill, the rate of flow being regulatedby turning handle it on vertical stem H, which stem projects aconvenient distance above the operating floor. The lower end it of stemIT is attached to the crusher-feeder flow control mechanism at I9 (Fig.2) The material fed to the mill is ground in usual manner by impact ofhammers (Fig. 3) which are hinged to pivot bars 21 carried by radialarms 22 mounted upon shaft 23 for rotation therewith. The mill shaft 23,connected to a 3,600 R. P. M. motor (not shown), is journaled in a pairof bearings 25 (Fig. 1) attached to vertical side walls 25 of the lowersection of the mill housing. The side walls 25 are tied together belowthe crusher-feeder by an inclined bottom plate 26 (Fig. 3) whichdelivers the flow of unground materials to the grinding chamber throughthe inlet opening 21.

With further reference to Fig. 3, the removable cover section 28 overthe grinding chamber comprises a pair of semi-circular side walls 29,the periphery of which is welded to arcuate plate 353. The walls 29 arealigned vertically above side walls 25 of the bottom section of the millhousing, the upper and lower sections having flanges 3i and 32respectively (Fig. 1) that are clamped together on parting line 33 toprovide dust-tight construction around the hammer rotative element. Thelowermost end 3c of arcuate plate 35 (Fig. 3) extends below the partingline 33 and is welded to cross bar 35 which bar is removably securedbetween side walls 25 of the lower section of the housing.

Underlying the hammer rotative element in the periphery of the grindingchamber is a rectangular opening 55 for the efilux of ground material,which opening is defined by two arcuate ribs 31 welded to side walls 25,the lower edge 38 of crossbar 35, and the lower edge 35 of inclinedreceiving plate 25. Removably clamped over the border elements thatdefine the opening 36 is an arcuate working screen 4B through which thereduced product is graded as it escapes from the grinding chamber, thisscreen being held in working relation with the hammer rotative elementby a clamping mechanism that will be subsequently described. The workingscreen 40 is subject to automatic removal and replacement by any one ofthe three similar idle screens 4], 42 and 43 shown stacked in layerformation above cover section 28 of the mill housing. Likewise,regardless of which screen is in the mill at the beginning of the screeninterchange cycle, any one of the three other idle screens may beselected for direct interchange therewith.

The compartment i l, Figs. 3 and 6, which receives the efnux of groundmaterial that is graded through the working screen, has an inclinedbottom plate 45 (Figs. 1 and 3) which joins with the side walls 25 toform a gradually increasing U-shaped trough 55 (Fig. 6) which connectswith the circular outlet opening 4'! in the vertical cross wall 48 ofthe housing, the opposite end 49 of plate 45 being flanged upwardly tojoin with receiving plate 26. From opening 41 the reduced materialtravels through the tubular element 55 (Fig. l) to inlet of fan iii. Thetop of the efiiuxreceiving compartment 44 is covered by plate 5! (Fig.3) that is flanged upward at 52 to provide an open passageway 53 throughwhich any screen may be translated into or out of compartment 44. Thispassageway is made dust tight, while the 4 working screen is held inoperative relation with the hammer rotative element, by a closure thatoperates automatically in timed relation with the screen-translatingmechanism, as will be subsequently described.

The several idle screens stored above the mill housing (Fig. 3) havetheir distal ends hanging downwardly into the passageway 53 in looselayer formation, so that any screen may be lowered into the mill housingor withdrawn therefrom without undue friction between abutting screensurfaces. Also, it will be seen that the proximal end 54 of workingscreen 40, and likewise any screen that may be introduced into the millhousing, projects above the distal ends of the idle screens. Thisoverlapping relation of the working screen with respect to the idle.

screens makes it practical to move any screen upwardly or downwardly,within fixed limits, without danger of the ends of the screens foulingwith each other.

Screen-clamping mechanism As shown in Fig. 3 the working screen 40, orany screen interchanged therewith, is removably held over the outletopening 35 and against stationary ribs 3?, cross bar 35, and the lowerend of receiving plate 26 by means of a power-operated toggle-clampingmechanism, which is further illustrated in Fig. 7 with the'screenremoved. This clamping mechanism includes three vertical arcuateclamping bars 55 which are formed con-- centrically with respect tostationary ribs 31, their lower ends 55 being hinged to pivot bar 51supported by side walls 25 of the housing, while the upper ends arewelded to cross header 58 to form a three-legged frame (Fig. 6) that maybe swung inwardly to clamp the positioned screen to the border elementsthat define the peripheral screen opening 36; and contrawise, as shownin Fig. '7, this three-legged frame may be swung outwardly to releasethe screen for removal and interchange. The horizontal header 58, asbest shown in Fig. 3, is angular in cross section, the inclined leg 59being formed with a lower marginal edge that bears upon the outer faceof the screen on a line that is directly opposite cross bar 35, therebyforming a dust-tight joint between screen and elements 59 and 35 incontact therewith. The upper marginal edge of vertical leg 60 of header58 seats against resilient rubber gasket 6!, which gasket is secured tounderside of cover plate 5|, thereby providing a dust-tight closure forscreen passageway 53 when the screen is clamped in working relation withthe hammer rotative element. Also, it will be seen that the closing andlikewise the opening of passageway 53 takes place simultaneously withrespect to the clamping and releasing of the screen.

The toggle mechanism (Figs. 3 and 6) that automatically clamps andreleases the working screen is actuated by shaft 62 which has its endsjournaled in side walls 25, the near end projecting beyond the wall toreceive power-driven means that rocks the shaft to and fro through anangle of approximately 30 as will be described. Upon shaft 62 is mounteda tubular sleeve 63 secured thereto by pin 64 or other means, thissleeve having three upwardly projecting arms 65 that are aligned toengage and support cross shaft 65 which swings therewith when shaft 62is moved. In pivotal engagement with shaft 56 are three plain links 61that have their upper ends pivotally engaged to cross shaft 68 which ismovable therewith. The linkage which operates the screenclampingelements further includes: three" bellcranks 69, details of whichareshown in Figs. 4 and 5. Theouter end of each bellcrank has an opening76 which pivotally engages shaft 68, and an opening on the oppositeendwhichpivotally engages shaft 72. carried by clamping bars 55 (Fig.7). Formed integral with each bellcnank 69 is an upwardly projecting earI3 which has an opening 14 that receives'the'body'of capscrew I5 inloosely fitting relation as bestshown-in Fig. 7-, the threaded end. ofthe capscrew being adjustably screwed into the threaded opening I5 of.boss TI on leg 59 of header 58. To make the clamping mechanism effectivewhen closedupon screenslof different thicknesses, acoiled compressionspring 18 is assembled over capscrew 15, the lower end of the springseating against ear 13 of the bellcrank, andthe upper. endagainstbosscar 73, as indicated at 19 in Fig. 3, then spring is automaticallycompensates for any variation in thickness of the several screensemployed in the mill. In addition, spring 18 effects a suddensnap-action release of the screen when the shaft I52. is turnedclockwisea few degrees. After the screen is released, the head ofcapscrew I5 bears against the lower face of ear 13 of bellcrank 69, asmay be seen in Fig. 7.. When the screen is fully released; clamping bars55 are swung outwardly away fromribs 3'! to form the open space 85'therebetwcen, this space. being relatively wide at the top and narrow atthe bottom. The outward swing of clamping bars 55 is limited by makingcontact at 3] with sleeve 63 on shaft 62. Upon the projecting end. ofshaft 62 is mounted the bifurcated arm 82 (Fig. l), which arm is madeintegral with hub 83 this hub being pinned at 84 (Fig. 6) to shaft 52,so that when arm 82 is tilted downward, as shown in Fig. 1, thescreenclamping mechanism is. closed. Contrawise, when arm 82 is tiltedupward, as shown in dot and dash lines, the screen is released forremoval from the mill; The means employed to tilt arm 82 up and downthrough an angle of about will be subsequently described.

Slipclutch mechanisms Referring to Figs. 1, 2 and 11, the power thatdrives the screen-clamping mechanism, and likewise the screentranslating mechanism, is obtained from shaft which is journaledinbearlugs 86 mounted upon cover section 28 of the grinding chamber.Shaft 85 is. driven by the reversible three-phase motor 8? which ismounted within the mill housing as shown by broken lines in Fig. 1. Thepower from motor 81 is transmitted to shaft 85' by anysuitablespeed-reducing means, the mechanism illustrated includingcountershaft 88 upon which is mounted sheave 59 driven from sheave 90 onthexmot'or'byv-belts 9!, the countershaft beingsupported by'the millhousing in any suitable manner. From sprocket 92 on countershaft 88thepower. is transmitted by chain belt 93 to the. relatively large:sprocket 94 mounted on end section 95 ofi shaft 85. The

hub. 9.6- of sprockets! lis bored: for? axialislipifitxlon shaft 85, theshaftibeingsdriven;byvaifeatherrkey (not shown) that engagesthe keyway'91 (Fig. 11) in the shaft; Also, bored for slip fit and mounted on endsection 95-of theshaft (Fig: 2) is a series of 'five'smaller sprockets 9B te l 02* which drive chains I 03- to I01 respectively, the chain 103being belted to a relativelylargesprocket. I08 which operates thescreen-clamping mechanism and also serves-as a rotative timing elementfor the electricalcontrols as will be explainedi On the opposite endsection IOE- of shaft are mounted four sprockets I Ill-to lfI t thatareduplicates of sprockets 99 to' I02 on-opposite' end of shaft, and tosprockets III) to H3 are belted chains H4 to Ill'respectively. Thechains I IW- II4, I55-II5, IllG-I-IG and IIJT-II'I are paired to travelin unison and are'employed for translating the screens-40" to 43respectively intoand out of themlll, as Willbe-fur-ther explaineoli Toeach of the driving sprockets mounted on shaft 85 is appliedanindividual slipclutch mechanism that transmits a-predetermined amountof torque before slippage takes place, this torque being the same forall of the sprockets. With shaft 85 turning ineither direction, thepaired sprockets associated with anyscreen slip inunison when the screenis standingstill, andunder certain conditions all of theclutchmechanismsmay slip simultaneously." Inasmuch as the several clutchmechanismsare-all identical in construction and operation, only one willbe described, and for the purpose'of illustration the one applied tosprocket III) has been selected. The slipclutch mechanism that drivessprocket IIIl, Fig. 11, includesapair of' fiber friction disks IIB boredfor running fit on shaft85i and a pair of metal disks H9, each of whichis formed with bore I20 having an inwardly projecting spline I21 whichslidably engageskeyway 9-1 in the shaft, so that the disk rotateswiththe shaft regardless of its axial position thereon. These disks areassembled on the shaft in symmetrical relation with respect to sprocketIII], the fiber: disk'being sandwiched between the metal'diskandsprocket and in frictional contact with both, so that when theassembly is subjected; to axial. thrust from opposite directions, thesprocketiscausedlto rotate with the shaft. The amount of: torquedelivered by the sprocket tothechainthereon, before slippage takesplace, depends upon the amount of axial pressure applied to theassembly.

With further reference: toFig; 11; the nut" I22 in engagement withthreaded end H19: of shaft 85 provides a convenient means-for regulatingthe amount of axial thrust that is simultaneously applied to the severalslipclutch mechanisms as-' sembled in multiple upon the end section of.the shaft. The nut I22 seals against auxiliary metal disk I23, whichdisk is bored for slip'fit on the shaft and held in spacedrelationfromthe outer most metal disk I I9 by three or 'more coiled com pressionsprings I24, these springs beingheldin place by assembling one end oversuitable inwardly projecting bosses I25can'ied by'enddisk I23. Thrustcollar I26 (Fig. 2) takes the reaction of nut I22 on end section ofshaft 85*. The sprocketdisk M on endlsection 95 of the shaft serves thesame purpose as-diski 4233' on: the op:- posite end section, anddisk 94is. held in spaced relation from adjacent splineddisk I I9 by coiledsprings I24 in the same manner, so that when nut I 27 is adjustedto bearagainsthub 96 of sprocket 94, the multiplev slipclutch' mechanisms: are:sub

j ected to' the necessary axial thrusuin sameimam Screen-translatingmechanisms To the proximal end of each of the four screens is attached ahorizontal drawbar I23, Figs. 8 and 10, which projects beyond sides ofthe screen to engage translating chains associated therewith. DrawbarI28 is attached to screen 40 by means of centrally disposed hinge buttsI29 and I38 welded to the drawbar and screen respectively, the buttsbeing detachably secured together by removable pivot pin I3I.Translating chains I04 and H4 associated with screen 40 each carry anattachment I32 which is formed with a rectangular opening I33 asshown inFig. 9, this opening being adapted to receive the end of drawbar I28 inloosely fitting relation, so that when the paired chains travel inunison the screen is moved therewith. Consequently, the screen istranslated into the mill housing when the chains travel in a clockwisedirection, and contrawise, from the housing when the travel iscounterclockwise. In like manner screens 4!, 42 and 43 are translated bypaired chains I-I I5, I08I IE and I0"II I? respectively. The downwardtravel of the screens is limited by a pair of vertical stops I34-I34(Fig. 3) upon which the drawbar I28 comes to rest when the screen ispositioned within the mill ready for clamping. These stops also form theopposite end walls of screen passageway 53. The upward travel of thescreens is also limited by the drawbars coming to rest against verticalstop plates I35--I35, which plates are welded to cover section 28 of themill housing. After the screen has reached the limit of its travel ineither direction, the slipclutch mechanism associated therewith mustslip until shaft 85 comes to a standstill.

Screen-restmz'ning mechanisms When shaft 85 rotates in a clockwisedirection the idle screens are all urged by their respective slipclutchmechanisms to move downward into the mill housing. As only the selectedscreen may be allowed to move downward into the mill, it becomesnecessary to apply individual restraining means to each of the severalscreens, this means being subject to solenoidal release as will beexplained. The restraining means (Figs. 3, 8 and 17) comprisesspring-urged latches I36 to I39 for screens 40 to 43 respectively. Tothe upper edge of each draw bar I28 is welded a flat centrally disposedear I40 that has an elongated opening I4I which is adapted to engage therestraining latch associated with the screen. As the latches are allsimilar in construction and operation, only latch I36 (Fig. 3) will bedescribed in detail, this latch being formed as a bellcrank with bodywelded to cross shaft I42 which has opposite ends pivotally mounted invertical stop plates I35 so that the latch may be tilted in a verticalplane. The upper end I43 of the latch is formed as a pointed hook thatengages opening MI in drawbar ear I40 when drawbar I28 is positionedagainst stop plates I35. The pointed hook I43 is urged downward intoopening MI by action of coiled spring I44, this spring being tensionedbetween arm I45 of the latch and cover plate I43 which spans stop platesI35. Thus engaged by latch I36, screen 40 is securely restrained fromdownward movement into the mill while shaft 85 is rotating in clockwisedirection. The means employed to free the screen from the latch includesvertical pushrod I41 which is operated by a solenoid, as will be furtherexplained, the lower end of this pushrod being pivotally attached to theouter end of arm I45 of the latch, so that when the latch is tiltedcounterclockwise the hook I43 is raised to clear drawbar ear I40. Inthis manner similar pushrods (Fig. 17) I48, I49 and I50 are employed toactuate latches I31, I38 and I39 respectively.

Solenoidal release of selected screen Referring more especially to Figs.3 and 17, it will be seen that latches I35 to I39 are operated byindividual solenoids I5I to I54 attached to vertical pushrods I41 to I50respectively. These are conventional solenoids with an iron plunger thatmoves downward when energized. They are mounted upon plate I46 which isprovided with an opening (not shown) below each solenoid through whichthe plungers connect with the vertical pushrods. Only one of thesolenoids may be energized at a time, and this solenoid remainsenergized until the bifurcated arm 32 is tilted downward to clam thepositioned screen in operative relation with the hammer rotativeelement. After the solenoid is deenergized, the spring-urged latch tiltsclockwise to resume its normal position in readiness to engage thescreen associated therewith when the screen is withdrawn from the mill.The electrical circuits and the timing mechanism employed in energizingthe four solenoids will be subsequently described in connection with thewiring diagram shown in Fig. 18.

Tracks for screen-translating chains To translate the screens up anddown through the screen passageway 53 without flexing, and to avoidundue friction with each other and stationary parts or the mill housing,it becomes necessary to guide the proximal end of each screen and thedrawbar connected thereto over a fixed path, this path approximating thearc of a circle having its center located within the confines of thegrinding chamber. This is accomplished by providing a curved or arcuatetrack for each of the screen translating chains to travel upon, theseveral tracks being generally designed as assemblies I55 and I56 whichare rigidly attached to opposite side walls of cover section 28 of themill housing as shown in Figs. 1, 2, 6, 12, 13 and 14. The assembly I55,which is mounted on near side of mill, includes spacedapart track platesI5? to I60, the upper marginal edges of these plates serving as tracksfor chains I84 to I07 respectively. Likewise, assembly I56 includestrack plates IEEI to I65 for chains II4 to I II respectively. Referringmore especially to Figs. 12, 13 and 14, the lower ends of the curvedtrack plates are supported in common on stud I65 welded to adjacent wallplate of cover section. With stud I55 as a pivotal point, the uppersections of the several track plates in each assembly are fanned out infixed overlapping relation, so that the upper marginal edges of pairedplates I60-I84, I58I63, I58-I62 and I5I-I6I are positioned atprogressively higher levels in the order related. This arrangement ofthe track plates provides working clearance between the several drawbarsI28 when they are stacked above the cover section. This clearancedecreases as the arcuate tracks approach a common point of tangencydirectly over the screen passageway 53 (Fig. 3). In other words,regardless of which screen is in the mill, its drawbar will bepositioned in common as shown in dot and dash lines I86, Fig. 12.

'As illustrated in'Figs. 12 "and 16, "the screentranslating chains areconventional roller chains with rollers Iii-l tied together by pairedlinks Hill-468 and I'69-I69, the lower extremities of inside links I68overlapping the rollers and straddling the track plate such asldlythereby guiding the travel of the chain thereon. To further increasethe stability of the chains traveling over the arcuate tracks, theperiphery of each track plate, such as I51, is made with aplurality ofcircumferentially spaced G-shaped indentations I'1IJ into each of whichis assembled a small sprocket I1I that is positioned sothatits uppermostteeth engage the chain traveling on the track plate. As best shown inFig. 13, each sprocket is rotatively mounted on a shouldered stud I12riveted to ear I13 which ear is Welded to the track plate. The lower endof track plate I51 is Welded to ear I14 (Fig. 12) which engages studI65, thereby providing supporting means for the lower end of the plate.Also, mounted upon stud I65 for rotation thereon and aligned with plateIE1 is an idler sprocket 115 that is similar to sprocket I1! and whichserves the same purpose. Likewise, track plates I", I59 and I65! areprovided with idler sprockets HI and I15. The track assembly I56 is aduplicate of assembly I55 in all respectsexcept it is mounted upon theopposite side of cover section 28 in opposite hand relation, so thatfanned-out ends of track plates Ilse-454, Ids-4E3, let-I62 and i51-I6Iare paired to support the chains mounted thereon at progressively higherlevels.

To provide means for individually tensioning each ofthescreen-translating chains, such as chain 1%, the-lower span of thechain is carried over idler sprocket 115 as shown in Figs. 12 and 15,the sprocket being rotatably supported upon stud Iii riveted to plungerelement I18, the plunger'being slidably mounted for vertical adjustmentwithin the boxlike housing I19 attached to the adjacent side wall ofmill. The plunger is raised to tension chain m4 by adjusting setscrew I80 threaded into bottom I8I of housing Ii-e, the upper end of thesetscrew bearing against the lower end of the plunger. The chains I05,Iilt and lei are tensioned in the same manner, the several plungersassociated therewith being assembled in housing I19. Chains H4 to H1 onopposite side of mill are tensioned in the same manner.

Timing mechanism for screens It will now be recalled that when shaft62,Fig.

3, is rocked in a clockwise direction by tilting Sprocket I28 isrotatively mounted upon stud shaft Hi2 which is supported by near sidewall of the mill. This sprocket I08 carries an inwardly projectingcrankpin I 63 that tilts arm 82 up and down, the travel of thecrankpinbeing about 315 back and forth on circular are shown by dot andline I34. The-crankpin I83 is shown in cross section as a result of afragment of sprocket 1538 being deleted. While the crankpin is movingupward in counterclockwise direction, the working :screen is releasedfrom the ginning of the screen interchangeoycle. "The selected screen isreleased from its tilting latch while shaft I35 is turningcounter-clockwise, under which condition there is no strain on the latchas the reserve screens are being urgedaupward by the slipclutchesassociated therewith. The crankpin I33 is limited in its travel in'ibdthdirections by electrical controls appliedtoimotor 81 which willbepresently described.

The bifurcated arm82 (Fig. 1) is'fonnedwith upper and lower forks I85and I86 respectively, these forks being spaced apart vertically inparallel relation a distance'that'is approximatelyitwo to three timesthe diameter of crankpin I183. :The upper fork is made shorter than-thelower (fork, and the distal end of the lowerforkis turnedxupward toprovide finger I81 which serves 5355-3, positive stop against which thecrankpinrcomes to rest at the end of itsclockwisemovement, this alsobeing the end of the screen'interchangecycle. When the crankpin seatsagainstfinger 48:1, the bifurcated arm 82 is tiltedto its;lowermostposition, and the workingscreen .is-clamped ready for service. The openspace I88 'between' flnger I81 and the end of upper fork I185 providesagap through which the crankpin, when traveling counterclockwise,escapes from the confines of the two forks, the armc82 being tilted toits=uppermost position as shown by dot anddash lines. Continuing itscounterclockwiseitravel;thecrarikpin engages a spring-loaded armIfiilrwhich aCtuates single pole double-throw limit switch EH10 securedto nearside wall of the mill housinggits arm I89 being normallypositioned to maintain. motor 8'17 energized forcounterclockwise:rotation by means of holding coil I9! of'Fig. I8.iHol-izling coil IBI is released 'andopposite holdingxcoil 192 isenergized when arm I89 is engaged :by the crankpin, thereby reversingthe motor'for'clockwise rotation, and likewise shaft :-.8.5 and thecrankpin I83. The reversal ofrshaftafifidnstantly starts the previouslyreleased screen on itsrdown- 'ward journey into the mill. Holding coill92:con-

tinues to function until the end of "the :cycle, however, arm I89 oflimit switch I returns=to its normal position as soon as the crankpinhas traveled a few degrees in clockwise direction. e'In its clockwisetravel the crankpin re-enters gap I88 and tilts the bifurcated armdownwardthereby closing the clamping mechanism .upon :the interchangedscreen. The time interval involved in the screen clampingoperation:is'relativelyilong as compared with that required to releaseithe screen, which, as willbe recalled, is'a sudden snap action. Thissudden release of thescreen. speeds up its removal from the-mill.

With further'reference toFigs. land 18,:before crankpin I83 reaches thelimitof its clockwise travel, and likewise before bifurcated arin 82*istilted to its lowermost position, the lower edge ofthe bifurcated arm,engages the spring-loaded arm I93 of single-poledouble-throw limitswitch I 94, :which ISWitCh is :also mounted on meat-"side ofmillhousing. The engagement of arm 82 with switch arm I93 releasesholding coil I92 and interrupts the current to motor 81. After the motoris de-energized it continues to coast until the crankpin stops againstfinger I81 of the bifurcated arm. During this brief coasting period theslipclutch mechanism applied to sprockets 88 to I82 and II to H3 onshaft 85 are all slipping. The solenoid associated with the screen nowin the mill was simultaneously de-energized when holding coil I92 wasreleased to stop the motor. The electrical circuits employed incontrolling the motor, solenoids, and the pilot lights will be presentlydescribed in detail.

' Pushbutton controls and signal lights Referring to the wiring diagram,Fig. 18, the three-phase motor 81 is operated from line wires I95, I96and I91, and is energized for counterclockwise rotation at the beginningof each screen interchange cycle by manually pressing any one of thefour spring loaded pushbuttons I52, I99, 200.0r 20I that is not in adepressed position, these pushbuttons being associated with screens 4!],4|, 42 and 83 respectively. Each pushbutton operates a normally opendouble Z-point-make selecting switch that closes two circuitssimultaneously, one of these circuits lighting a signal lamp associatedwith the idle screen that has been selected for interchange with theworking screen in the mill. The other circuit energizes the solenoidthat releases the restraining latch that is associated with the selectedscreen. When the operator presses any one of pushbuttons I53, I59, 225and 2!, this simultaneously closes contacts 2&2 and 203, 204 and 205,206 and 201, or 258 and 269 respectively. The contacts 202, 2G4, 225 and288 are in the circuits that energize pilot lamps 2H), 2! I, H2 and 2I3,which lamps are associated. with screens 40, 4|, 42 and 43 respectively.The contacts 293, 205, 201 and 209 are in the circuits that energizesolenoids I5I, I52, I53 and I54 respectively, these solenoids beingassociated with screens 40, 4|, 42 and 43 as previously mentioned. Whenmotor 81 is at rest the current from line wire I95 flows throughsingle-pole double-throw limit switch I94 as a result of itsspring-loaded arm I93 being engaged with bifurcated arm 82. therebyholding blade 2M against terminal 255 from which the current flowsthrough the signal lamp associated with the screen that is in the mill,and thence the current flows to line wire I91 to complete the circuit.

Mechanically connecting the four pushbutton switches I98, i951, 280 and20! in common is a normally open switch blade 2I6 which is hinged onterminal 2I1 so that it may be momentarily closed against terminal 2I8when the operator presses any pushbutton associated with an idle screen.These pushbuttons are so arranged and interlocked that when the selectedpushbutton is pressed, it first releases any other pushbutton that maybe in a depressed position as a result of the prior screen interchange,and then the selected pushbutton locks itself mechanically in thedepressed position until subsequently released by the operator when hepresses one of the other pushbuttons to effect another screeninterchange. The signal lamp associated with the ex-working screen isextinguished when the depressed pushbutton is released, andsimultaneously the signal lamp associated with the selected screen isener gized as a result of the operator pressing the selected pushbutton.lighted for only an instant, or until motor 31 has However, this lampis.

turned a'few counterclockwise revolutions to raise crankpin I83 and freebifurcated arm 32, which arm now swings upward with a snap action. Thisupward movement of arm 82 frees arm I93 of limit switch I94, the currentto the lamp being interrupted when blade ZI-t leaves terminal NB. Thissame lamp circuit is again energized at the end of the screeninterchange cycle, as will be later described.

Motor starting and reversing controls The only manual operation requiredto make the screen interchange is for the operator to press thepushbutton associated with the selected idle screen that is to be putinto the mill. The pressing of this pushbutton momentarily closes theswitch blade 216 against terminal 2 it! and energizes holding coil I9 I,the flow of the current bein from line wire I through closed switch 226,

contacts 2L9 which are operated by heater coilsmagnetically closes thefour ganged contacts 223,

22A, 225 and 226 simultaneously. The closing of contacts 223 shunts thecurrent around switch 2H; and keeps holding coil I9I energized afterswitch blade 2E6 has resumed its normally open position. The closing ofcontacts 22%, 225 and 225 delivers current to motor 81 from line wiresI25, I95 and I91, and the motor starts in a counterclockwise direction,the crankpin I83 being driven in the same direction. After the motor hasturned a few revolutions and crankpin I23 has traveled upward a shortdistance, the bifurcated arm 82 swings upward with a snap action as peviously explained, thereby releasing the springloaded arm I93 of limitswitch I94 and swinging blade 2M to terminal 221. This completes thesolenoid circuit from line wire I95 through limit switch Hi4 and theclosed pushbutton contacts to line wire I91, the solenoid associatedwith the selected screen now being energized and the screen freed fromits restraining latch. Simultaneously, when blade 2 I4 contacts terminal221 the wire leading therefrom to holding coil I92 becomes ready tofunction, and holding coil I52 is energized the instant the circuit iscompleted through limit switch 595, as will be presently described.

After leaving the bifurcated arm 82 the crankpin continues itscounterclockwise travel until it engages the spring-loaded arm I89 oflimit switch I96, during which time interval the exworking screen iswithdrawn from the mill. When blade 228 leaves terminal 229 in limitswitch use, this de-energizes holding coil HI, and, when the bladeswings over to terminal 235, this completes the circuit that energizesholding coil I92. The de-energization of holding coil I9l releases thefour ganged contacts 223, 224, 225 and 225, and the motor stops with thecrankpin in engagement with arm I89 on limit switch I 56. The energizingof holding coil I92 magnetically closes ganged contacts 23I, 232, 233and 235 simultaneously. The closing of contacts 23L 232 and 233 permitsthe current from line wires I85, 95 and Isl to flow through the motor inreverse phase relation, thereby energizing the motor for clockwiserotation. The closing of contacts 232 shunts the current around limitswitch I98 so that holding coil I52 remains energized. After crankpinI53 has traveled upward a short distance, and has accuses disengaged:springeloaded arm L182 ofilimit switch I90, the switchblade 228-returnsto:its normal position in contact withterminal 229. The motor continuesto rotate in clockwise direction until crankpin I33 re-engagesbifurcated arm '32 and tilts it downward to re-engage arm I33 of limitswitch I94, the blade 2M swinging away from terminal 2 2 I therebysimultaneously interrupting the flow of current through holding coil.492 and the solenoid which Was energized at the beginning of the screeninterchange. The daenergizati'onofholdingcoil 92 permits gangedcontacts23I, 252, 23$.and 23d toopen and :de-energizethe motor, this actiontaking placea brief interval of time before crankpin 83 comes to rest-against finger It! on the bifurcated arm. The motor continues to coastuntil .the friction of the slipping clutches onshaft .35 brings it to astandstill.

Example illustrating scr en interchange cycle Any one of the fourscreens that may be in the mill and clamped ready for service is subjectto replacement by any one of the other three screens by simply pressingthe pushbutton associated with the selected idle screen. Therefore, theelectrical controls illustrated in wiring-diagram, Fig. 18, must bedesigned to effect a total of twelve screen-interchange combinations,all of which operate on the same basic cycle. Consequently, it will benecessary to describe in detail only one screen interchange, and forthis purpose idle screen 42 has been selected for introduction intothe-mill to replace working screen 353 which is now clamped in operativerelation with the hammer rotative element as shown in 3. As a result ofthe preceding screen interchange, pushbutton I95 is in a depressedposition and the entire electrical control system is at rest with theexception of signallamp 213 which is lighted-to indicate that screens-l3is in the mill. The current for lamp ZIil flows from line wire I35through junction 235, lead 23-3, overload protection contacts 2N, safetyswitch 222, lead 233 to junctioniilfi thence through lead 239 to limitswitch 534 which hasits spring-loaded blade 22d closedagainst terminal2I5. From terminal ZIE lead Ztil conducts the current to pushbuttonmake-contacts 282, through lamp 22B, lead 2 H, thence to junction 242with line wire Isl, thereby completing the circuit for lamp 2m whichremains lighted. as long as pushbutton $28 is depressed.

To start the screen interchange cycle, whereby working screen ili .nowin the mill is replaced by selected screen 32, the operator simplypresses pushbutton 22% thereby simultaneously releasing depressedpushbutton I88 and momentarily closing switch 2% against contact .2I'8.As :pushbutton 206 remains ina depressed position, the two-pointmake-contacts 2dr; and'2fil areclosed and remain closed until the nextscreen interchange. While switch ZIE is momentarily closed againstterminal 2 I8 the current from line wire I35 is carried through junction235 with lead wire 236,norma1ly closed'switches2I9 and1222, lead 23'?through switch 2H5, lead 243, holding coil I9I, lead 254 to terminal 229of limit switch I98 against which blade 228 is normally closed, thencethrough lead 245 to junction 24% .to line wire J91, thereby completingthe circuit between lines I95 and I9! which energizes holding :coil I SI andmagneticallycloses the-.four gangedcontacts 223,224, 225-.and 226.

ill

When contacts #23 are .;closed this :shunts out thetmomentarycontactlIS, so that when switch 2I'6 is again opened, the :holding coillei will remain energized :to maintain ganged contacts 223, 224, 225and226 closed. As soon as these four contacts .are'closed, thethree-phase current from lines I95, I96 and I97 flows through contacts224,;225 and 226 :respectively. From contact 22 thecurrent flows throughlead 24? to heater coil 220,.and then throughlead Mil-to motor 8?. Fromcontacts .225 the lead 249 goes to the motor. From contactsJ226the lead250. goes to heater'coil 22Iifrom which'the current goes-to motorthrough lead :25I. This completes the three circuits to the "motor whichis now energized for counterclockwise rotation.

.It'willnow'be recalled that crankpin E83 (Fig. 1) carried lay-sprocketI03 rotates in same direction as motor 87, consequently, the cranlrpinstarts traveling counterclockwise when holding coil: I9I isenergizedatLthe beginning of thescreen interchange cycle, thereby tilting thebifurcated arm 82 :upwardly to release the screen-clamping mechanismthat holds screen it, which screen starts its upward journey as soon asfreed from the clamping mechanism. In addition, when arm is tiltedupwardly it frees the springloaded arm I93 oflimit switch It? so thatblade 25 i is moved to contact terminal 22?, which, through lead 252,conducts the flow'to contacts 2%? of pushbutton 2%, these contacts beingmechanically maintained in closed position, as previously explained, sothat the current may iiow through lead253 to solenoid I53 associatedwith screen 42. From solenoid I53 the current is car ried through wire245 to junction 2 56- and line wire Iii! to complete the circuit,thereby energizing solenoid 1153 which hits the restraining latch I33,and releases screen 42 which is now free tostart its downward journeyinto the mill housing at'the instant'the motor is reversed for clockwiserotation. The crankpin i8 3, continuing its counterclockwise travel,engages arm we of limit switch I 99, during which time interval screen40 is completely withdrawn'from the mill. housing and positioned so thatcar I643 on drawbar I28 engages thespring-urged restraining latchEngagement of the crankpin with arm its or" the switch I swings blade223 from contact 22$ to contact-.235). When blade 228 leaves contact22.9,the circuit through holding coil is! is broken, therebyreleasingcontacts 223, 22%, 225i and 228 and disconnecting motor 8'! from itssource of energy.

Withblade 228 of limit switch tell in contact with terminal 238, asmentioned in preceding paragraph, motored! is again energized, this timethedirectionof rotation being reversed or clockwise. The reversal iseffected by current from line wire I flowing through branch 2%, normallyclosed switches '2IS and 222, lead 23ft, junction'2'35, branch 239thence to limit switch I24 having blade 2M normally held in. contactwith'terminal 22?, then through lead 252 to June tion EMand IeadZES toholding coil I32, lead 253 t0'1i1nit switch rec having blade in contactwithterminallZfifi as a result of engagement of crankpin I33 with armI33. From blade 228 the current .fiows through lead 255 to junction 2-16with line wire 19?, thus completing the circlosesthe fourgangedcontacts'flt'I, 232, 233 and 234. With" contactv 234 closed, 1 thecurrent nowing through :holdingucoil I92 vis shunted across I from wire256 to junction 242 with line wireIISI, thereby maintaining holding coilI92 energized after blade 228 of limit switch I92 has been moved fromcontact with terminal 230 to engage terminal 229, which action takesplace as soon as crankpin I83 disengages the spring-urged arm I89 ofswitch I93.

With contacts 23I, 232, 233 and 234 closed by action of holding coil I92the three-phase current is carried from line wire I95 to junction 251,through lead 258, closed contacts 23I, lead 259 to junction with 250,thence through heater coil 22I to motor 81. From line wire I26 thecurrent flows through lead 260, closed contacts 232, lead 23I tojunction with wire 249 which is connected to the motor. From line wireIt! the current flows through lead 262, closed contacts 233, lead 263 tojunction with wire 24?, and then through heater coil 22!] to motor 81.Energizing these three circuits reverses the motor for rotation in aclockwise direction. Simultaneously crankpin I83 starts on its returnjourney in a clockwise direction and screen 42 starts its downwardjourney into the mill housing, it coming to rest when its drawbar I28engages stops I34 (Fig. 3). Immediately following the arrival of screen42 in position to be clamped for service, the crankpin, havingre-entered gap I38 of the bifurcated arm, engages the lower fork I85 ofthe arm and starts tilting it downwardly, this action clamping screen 42in operative relation with the hammer rotative element as previouslydescribed. Before arm 82 is tilted to its lowermost position, lower forkI85 engages arm I93 of limit switch I94 and swings blade 2I4 fromterminal 221 to 2I5, thereby interrupting the current flowing throughholding coil I92 and slenoid I53, and releasing contacts 23I, 232, 233and 234 which action simultaneously stops the motor and lights signallamp 2E2 to indicate that screen 42 is clamped ready for grindingservice. The circuit for signal light 2 I2 is same as the circuitpreviously described for light 2W except the current flows throughpushbutton contacts 206 instead of contacts 222, and light 2I2 remainslighted until screen 42 is withdrawn from the mill housing, or thecircuit is interrupted by opening switch 222.

What I claim is:

1. In a hammer mill or the like including a housing, an arcuate screenwhich is one of a plurality of similarinterchangeable screens removablefrom and insertable therein, means attached to the housing forsupporting the screens exteriorly thereof, an opening in the housingthrough which a selected screen may be translated, a mechanism forclosing the opening, a mechanism for translating the selected screenthrough the opening, and motor means for actuating said mechanisms intimed relation, said means including an oscillatable element.

2. In a hammer mill or the like including a housing, a screen which isone of a plurality of interchangeable grading screens removable from andinsertable therein, an automatic mechanism for removing any screen ofthe plurality that may be in the housing and inserting a selected screenof the plurality in substitution therefor, said mechanism including acombination a pair of sprocket chains associated with each screen, asprocket for driving each chain, a motor-driven reversible shaft uponwhich the said sprockets are mounted for rotation. therewith or relativethereto, said sprockets also being mounted for axial movement relativeto the shaft, and a 16 spring-urged frictional driving connection: be'--tween the shaft and each sprocket.

3. The combination as cited in claim 2 wherein the maximum torquetransmitted by the driving connection is varied by adjusting meanscarried by the shaft and rotatable therewith.

l. The combination as cited in claim 2 wherein the driving connectionsassociated with the paired chains slip simultaneously.

5. The combination as cited in claim 2 wherein the driving connectionincludes a driving disk mounted on the shaft adjacentto the sprocket forpositive rotation with the shaft and axial movement relative thereto, anintermediate disk mounted between the sprocket and the driving disk forrotational and axial movement relativeto the shaft, and resilient meansfor forcing the driving disk and sprocket axially towards each other tocause said sprocket to rotate with the shaft.

6. In a hammer mill or the like including a housing, a screen which isone of a plurality of interchangeable screens insertable therein andremovable therefrom, means associated with the housing for supportingthe reserve screens thereabove in an established order, an opening inthe periphery of the housing into which any selected screen may beinserted, a screen inserted in the opening, and means for maintainingthe inserted screen in the established order with respect to the reservescreens thereabove, the said means being the distal ends of the reservescreens hanging loosely in overlapping relation with proximal end of theinserted screen.

7. In a hammer mill or the like including a housing, an arcuate screenwhich is one of a plurality of interchangeable metal screens insertabletherein and removable therefrom, an opening in the housing through whichany selected screen may be translated, a screen inserted in the housing,and means for supporting the reserve screens in loose-leaf formationwith their proximal ends in spaced apart relation and their distal endsin metal-to-metal contact, said supporting means being the housingstructure.

8. In a hammer mill or the like including a housing, a screen which isone of a plurality of interchangeable screens insertable therein andremovable therefrom, an opening in the 110115- ing through which anyselected screen may be translated, a reversible mechanism fortranslating the selected screen through the opening, said mechanismbeing operated by a motor, a source of electrical energy to the motor,an active screen inserted in the housing and the motor at rest, manuallyoperated electrical controls for starting the motor in a predetermineddirection to remove the inserted screen, and electrical contactsassociated with the screen translating mechanism for automaticallyreversing the motor after removal of said screen.

9. The combination as set forth in claim 8 wherein the electricalcontrols include a normally closed spring-loaded limit switch, and meansfor opening the switch to automatically de-energizing the motor aftercompletion of the screen interchange, said means including anoscillatable element which is actuated by said motor.

10. In a hammer mill or the like including a housing, a screen which isone of a plurality of interchangeable screens insertable therein andremovable therefrom, .an opening in the housing throughv which aselected screen may be translated, a reversible motor-driven mechanismfor removing the active screen and inserting the selected screen, asource of energy to the motor, manually operated electrical controls forstarting the motor to eiiect a screen interchange, said controlsincluding a switch which closes two pair of contacts simultaneously, asignal lamp associated with each of the several screens, and means forenergizing the lamp associated with the inserted screen while thebalance or" the electrical system is at rest, said means being one pairof the closed contacts.

11. In a grinding mill or the like including a housing, a rotativehammer element which reduces material fed thereto, a screen supported inoperative relation with the rotative element, said screen being one of aplurality of similar screens interchangeable therewith and positionableupon the screen supports in like operative relation, ascreen-translating mechanism for automatically removing the operativescreen and positioning any selected screen of the plurality insubstitution therefor and in like operative relation, a rotative elementfor timing the operations of the screen-translating mechanism, andreversible power-driven means in common for actuating the timing elementand the screentranslating mechanism.

12. The combination as cited in claim 17.. which includestorque-responsive means for establishing a driving connection betweenthe power driven means and the screen translating mechanism, said meansbeing a slipclutch.

13. In a hammer-grinding mill or the like in cluding a housing intowhich is inserted an active screen through which the eillux of reducedmaterial is graded, said screen being one of a plurality of similarscreens interchangeable therewith and positionable in substitutiontherefor, means for supporting the reserve screens exteriorly of thehousing, a reversible screen positioning mechanism for replacing theactive screen by any selected reserve screen, power-operated means foractuating the screen positioning mechanism to effect the screeninterchange, a source of electrical energy, and electrical controlsassociated with each of the several screens which may be manuallyoperated to select the reserve screen prior to the interchange.

14:. The combination as cited in claim 13 wherein the power operatedmeans is an electric motor having reversing controls, said controlsbeing actuated automatically by rotative means driven by the motor.

15. The combination as cited in claim 13 which includes a rotativetiming element associated with the screen-positioning mechanism, areversible electric motor for actuating the timing element and thepositioning mechanism, a source of energy to the motor, and electricalmeans for controlling the direction of motor rotation, said meanscomprising a pair of spring-loaded singlepole double-throw limitswitches which are actuated by the rotative timing element.

16. In a hammer-grinding mill or the like in cluding a housing intowhich is inserted a screen through which the efilux of the reducedmaterial is graded, said screen being one of a plurality of similarscreens interchangeable therewith and positionable in substitutiontherefor, a motordriven screen positioning mechanism for effecting aninterchange of any selected reserve screen with the active screen, asource of energy to the motor, and electrical controls for the motor,said controls including a manually operated switch for selecting thereserve screen that is to interchange with the active screen, and meansin common with the manually operated switches for start ing the motor,said means being a normally open switch.

17. The combination as cited in claim 16 wherein the screen-positioningmechanism includes a slip clutch and a solenoidally operated latchassociated with each of the reserve screens, the said latches beingadapted to hold. the reserve screens immovable while the selected screenis being interchanged with the active screen, and means for energizingthe solenoid to release the selected screen, said means being themanually operated switch.

18. In a hammer-grinding mill or the like including a housing, a screenwhich is one of a plurality of interchangeable grading screensinsertable therein and removable therefrom, an opening in the housingthrough which any selected screen of the plurality may be inserted, areversible mechanism for translating the selected screen into thehousing, said mechanism includ ing an oscillatable clamping elementpower driven means for actuating the said mechanism, a source ofelectrical energy, an electrically operated indicator associated witheach of the several screens for visually indicating which one of thescreens is inserted in the housing, said indicators being stationedremotely from the mill, an electrical circuit for each indicator, aswitch in each indicator circuit, means for closing the switchassociated with the selected screen, a master switch in common with allthe indicator circuits, and means for operating the master switch, saidmeans being the cscillatable clamping element.

19. In a hammer-grinding mill or the like including a housing into whichis inserted an arcuate screen through which the eiiiux of reducedmaterial is graded, said screen being one of a plurality of similarscreens interchangeable therewith and positionable in substitutiontherefor, means carried by the housing for supporting the reservescreens thereabove in juxtaposed nested relation, an opening in thehousing into which a selected screen may be inserted and removed, areversible mechanism for removing the active screen from the housing andreplacing it with any selected reserve screen in substitution therefor,and motor means for actuating the reversible mechanism.

20. In a hammer-grinding mill of the type that employs interchangeablegrading screens, a housing having a grinding chamber in which isjournaled a rotative hammer element for reducing material fed thereto, acompartment which receives the reduced efilux from the grinding chamber,an opening in the periphery of the grinding compartment whichcommunicates with the efilux-receiving compartment, a screen removablypositioned over the opening in overlapping relation With the borderelements that define the opening, a reversible mechanism for clampingthe positioned screen to the border elements and holding said screen inoperative relation with the hammer element, and an electrically operatedindicant remote from the mill for visually indicating when thepositioned screen is clamped in operative relation with the hammerelement.

21. In a hammer-grinding mill or the like including a housing into whichis journaled a hammer rotative element for reducing material fedthereto, a screen inserted in the housing through which the efiiux ofreduced material is graded, said screen being one of a plurality ofsimilar reserve screens interchangeable therewith and positionable insubstitution therefor, means for supporting the reserve screens, areversible screen-positioning mechanism for replacing the operativescreen by one of the reserve screens, and an electrically operatedindicant remote from the mill for indicating which one of the severalscreens is positioned in operative relation with the hammer element.

22. In a hammer-grinding mill or the like including a housing into whichis inserted a screen through which the efiiux of ground material isgraded, said screen being one of a plurality of similar screensinterchangeable therewith and positionable in substitution therefor, ascreenpositioning mechanism for effecting the screen interchange toselectively vary the fineness of the material in the efiiux, an indicantassociated with each screen which may be seen by the operator from astation elevated above the mill housing, a normally open electricalcircuit for operating each indicant, a source of energy for eachcircuit, and means for automatically closing the circuit which isassociated with the inserted screen.

23. The combination as set forth in claim 22 wherein the indicantassociated with the inserted screen includes a lamp.

24. In a machine that employs a removable screen or the like, saidscreen being one of a plurality of similar screens interchangeabletherewith and positionable in substitution therefor, the combinationthat includes a mechanism for translating each screen to effect aninterchange of any reserve screen with the employed screen, a rotativeshaft in common for actuating the screen translating mechanisms, a,permanently engaged torque-responsive element for connecting each screentranslating mechanism to the shaft, said elements being mounted on theshaft for rotation therewith or relative thereto, and means supported bythe machine structure for restraining movement of the screens to cause aplurality of the torque-responsive elements to slip simultaneously.

25. In a hammer mill that employs arcuate grading screens, a housing, anopening in the housing into which a screen may be inserted, a screensupported above the housing by means attached to the mill structure, areversible mechanism for inserting the screen into the opening, meansfor actuating the reversible mechanism, and pivotal means for connectingthe screen to the said mechanism, said pivotal means being detachablefrom the screen.

26. In a hammer mill, a housing, said housing having a lower arcuateopening for discharge of material, an arcuate screen, movable into alower position to cover said opening and into a higher reserve positionexteriorly of the housing, guide means for directing travel of thescreen between the two positions, motor means for moving the screenbetween the two positions, including a pair of endless belts attached tosaid screen, and. means to drive the belts in unison.

27. In a hammer mill, a housing, a screen which is one of a plurality ofinterchangeable screens insertable therein and removable therefrom,means attached to the housing for supporting the screens exteriorlythereof, an opening in the housing into which a screen may be inserted,a mechanism for translating each screen into the opening, motor means incommon for operating the translating mechanisms, a slip clutch drivingconnection between the motor and each translating mechanism, said clutchbeing adapted to transmit a limited amount of torque, a selected screenmoving into the open ing, and means for holding the reserve screensimmovable against the pull of their respective slip clutches, said meansbeing a latch in engagement with each of the reserve screens.

28. The combination as cited in claim 27 wherein the latch is disengagedfrom the selected screen by solenoiclally operated means, thedisengagement being made prior to removal of the inserted screen.

29. The combination as cited in claim 27 which includes means forreleasing the latch from the selected screen to allow movement into themill, said means being a solenoid.

30. In a hammer mill of the type that employs interchangeable gradingscreens, a housing, a discharge outlet in the periphery of the housing,said outlet having border elements adapted to seat a screen, a screenpositioned over the outlet, motor means including an oscillatableelement for clamping the positioned screen to the border elements, saidmeans also being adapted to release the screen, and means for timing thereleasing and clamping operations, said means including the oscillatableelement.

31. The combination as cited in claim 30 wherein the screen-clampingmechanism includes means for spring-urging the clamped screen againstthe border elements of the peripheral opening, said means beingcompressed when screen is clamped.

32. The combination as cited in claim 30 wherein the means for actuatingthe screenclamping mechanism includes a torque-responsive slipclutch,said clutch being adapted to slip when the screen is clamped.

33. In a hammer mill, a housing, said housing having an arcuate outletfor discharge of material, an arcuate screen, movable into a lowerposition to cover the outlet and into a higher reserve positionexteriorly of the housing, an opening in the housing into which thescreen may be inserted, guide means exteriorly of the housing fordirecting the travel of the screen in an arcuate path between the twopositions, said means being supported by the housing, and motor meansfor moving the screen between the two positions.

34. In a hammer grinding mill, a housing, said housing having a grindingcompartment, an arcuate outlet in periphery of said compartment fordischarge of material, said outlet having border elements adapted toseat an arcuate screen, a compartment that receives efliux from thedischarge outlet, an opening in the eiilux compartment through which ascreen may be inserted and withdrawn, a screen supported exteriorly ofthe efliux receiving compartment by means attached to the millstructure, means for inserting the screen into the efflux receivingcompartment and positioning it over the discharge outlet, means forclamping the positioned screen to the border elements of the dischargeoutlet, means for closing the screen opening after the screen ispositioned, and motor means in common for actuating the said inserting,clamping and closing means in sequence.

35. In a hammer mill, a housing into which is inserted a grading screen,said screen being one of a plurality of similar screens interchangeabletherewith and positionable in substitution therefore, motor means forpositioning a selected screen in substitution for the inserted screen,

21 manually operated controls for selecting a reserve screen, a sourceof electrical energy for the motor, electrical controls for starting themotor, and means for operating said starting controls, said means beingthe manually operated selecting controls.

36. In a hammer mill, a mill structure including a housing, an arcuatescreen which is one of a plurality of similar interchangeable screensinsertable in the housing and removable therefrom, an opening in thehousing into which a screen may be inserted, a selected screen insertedin the opening and having one edge projecting therefrom, means forsupporting the reserve screens exteriorly of the housing and inoverlapping relation with the projecting edge of the inserted screen,said supporting means being the mill structure, a mechanism forwithdrawing the inserted screen from the opening while the reservescreens are standing still, and means for supporting said mechanism,said means being attached to the mill structure.

37 In a hammer-grinding mill or the like including a housing into whichis inserted a grading screen, said screen being one of a plurality ofsimilar reserve screens interchangeable therewith and positionable insubstitution therefor, a reversible screen-positioning mechanism forinterchanging a selected screen with the inserted screen, motor meansfor actuating the screenpositioning mechanism, a source of electricalenergy for the motor, and electrical controls for simultaneouslyselecting the reserve screen and starting the motor, said controlsincluding a manually operated pushb-utton switch associated with eachscreen and a normally open switch which is momentarily closed by theselected pushbutton to energize a holding coil that starts the motor.

38. In a hammer mill or the like including a housing, an arcuate screenwhich is one of a plurality of similar interchangeable screensinsertable in the housing and removable therefrom, means for supportingthe screens exteriorly of the housing in fixed relation with each other,said means including a stationary track, an opening in housing throughwhich a selected screen of the plurality may be translated, a mechanismincluding an oscillatable element carried by mill structure fortranslating the selected screen into the opening while the reservescreens are standing still, said mechanism being reversible for removalof the inserted screen, and stationary means attached to the millstructure for limiting travel of the outgoing screen.

39. In a hammer mill including a housing, an arcuate screen which is oneof a plurality of similar interchangeable screens removable from andinsertable therein, means for supporting the screens exteriorly of thehousing in a fixed order with respect to each other, said meansincluding a stationary track, an opening in the housing into which aselected screen may be inserted, a reversible mechanism for translatingthe selected screen into the opening while the reserve screens arestanding still, said mechanism also being adapted for removing screen,means for limiting movement of the screen-translating mechanism in bothdirections, said means bein stationary elements associated with the millstructure, and means for limiting travel of the screen, said means beingthe screen-translating mechanism.

40. In a hammer mill, a housing, .a screen which is one of a pluralityof interchan eable screens insertable therein, means for supporting thereserve screens exteriorly of the housing, said means being attached tothe housing, an opening in housing into which a selected screen may beinserted, a reversible mechanism including an oscillatable element forinserting the selected screen, means for supporting the reversiblemechanism, said means including a stationary track, guide means fordirecting travel of moving screen in a fixed path, said means includingthe track, and means for actuating the reversible mechanism while thereserve screens are standing still.

ARTHUR G. NICKLE.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,076,025 I-Iazle Apr, 6, 1937 2,076,297 Gray Apr. 6, 19372,227,090 Hughes Dec. 31, 1940 2,258,537 Calkins Oct. 7, 1941 2,328,170Schutte Aug. 31, 1943 2,360,892 Rench et al Oct. 24, 1944

